1. Technical Field
This invention relates generally to the batch processing of miniature electronic circuit components, including passive, two-terminal, ceramic capacitors, resistors, inductors, and the like. More particularly, it concerns a contactor assembly for electrically contacting a terminal on such a component or other device under test (DUT) as part of the batch processing for purposes of parametric testing.
2. Description of Related Art
The tiny size of electronic circuit components of interest herein complicates processing. Typically fabricated in parallelepiped shapes having dimensions as small as 0.020xe2x80x3by 0.010xe2x80x3by 0.010,xe2x80x3more or less, these difficult-to-handle components require appropriate equipment and precision handling techniques. What is sometimes referred to as a xe2x80x9ccarrier platexe2x80x9d holds many hundreds of the components upright in spaced-apart positions as the ends of each component are coated with a conductive material to produce electrical terminals. After adding terminals, a xe2x80x9ctest platexe2x80x9d holds the large batch of components for movement past a contactor assembly of a testing system for parametric testing purposes and eventual sorting. Thoughtful design of each of these components promotes efficient processing. Reference may be made to U.S. Pat. Nos. 6,204,464; 6,294,747; 6,194,679; 6,069,480; 4,395,184; and 4,669,416 for examples of some prior art component handling systems and testing techniques.
The contactor assembly is of particular interest. It is a device having an electrical contact that touches the DUT terminal as the test plate moves the DUT past the contactor assembly. It does so to complete an electrical testing circuit. One problem is that touching the DUT terminal improperly can physically damage the terminal. It can also produce a poor electrical contact that degrades test results.
Existing production testers often use xe2x80x9csliding contactsxe2x80x9d and/or xe2x80x9crolling contactsxe2x80x9d to perform the electrical and mechanical functions mentioned above. Electrically, the contacts should couple a test signal between testing components and the DUT terminal in a manner providing a sufficiently accurate electrical test. Mechanically, the contacts should press the contact against the DUT terminal with enough force to attain a good electrical contact despite the usual presence of a non-conductive oxide layer on the surface of the DUT terminal. Sufficient force causes the contact (e.g., a sliding leaf spring type of contact) to advance through the oxide layer to the underlying conductive material of the DUT terminal, and that reduces electrical resistance between the contact and the DUT terminal.
The problem is that forcing the contact against the DUT terminal can leave a mark or scratch on the surface of the DUT terminal. End users of the component often consider such scratches to be defects. Failure to achieve a good electrical contact, on the other hand, degrades test results. The electrical and mechanical functions are conflicting in those respects and existing contactor assembly designs exhibit varying degrees of success in alleviating the conflict. Thus, manufacturers engaged in batch processing of miniature electronic circuit components seek improvement in contactor assembly design and so a need exists for a better contactor assembly.
This invention addresses the concerns outlined above by providing a contactor assembly having at least three independently moveable contacts in side-by-side relationship that are spring biased toward the DUT terminal. Three contacts help insure that at least two of them contact the DUT terminal for lower serial impedance in series with the effective serial resistance (ESR) of the DUT. A preferred embodiment accomplishes spring biasing with constant force over a normal range of travel (e.g., one to three millimeters) to alleviate scratching concerns.
The illustrated embodiments achieve the foregoing and much more. Sliding contacts in the form of thin side-by-side blades having forward edges disposed toward the DUT terminal further facilitate multiple contacts. Insulation between contacts isolates the contacts from each other to enable Kelvin measurement techniques. An intermediate one of the three contacts may be held at a guard potential in order to help balance leakage currents, and the number of blades can be increased beyond three so that they can better conform to the shape of the DUT terminal. This xe2x80x9cmultipointxe2x80x9d technology reduces or eliminates the serial stray impedances with the DUT, while the xe2x80x9cguardingxe2x80x9d technology reduces or eliminates the effects of parallel stray impedances with the DUT. Multipoint technology works well for very low impedances. Guarding technology works well for very high impedances
To paraphrase some of the more precise language appearing in the claims, the invention provides a contactor assembly useable on a component testing system for electrically contacting a terminal on a DUT. That is done as the component testing system moves the DUT past the contactor assembly for parametric testing and eventual sorting as part of component batch processing. The contactor assembly includes at least three contacts that are referred to herein as first, second, and third contacts (i.e., three or more contacts). Each of the contacts having a respective one of first, second, and third forward edges for physically and electrically contacting the DUT terminal as the DUT moves past the contactor assembly. Three or more contacts help insure that at least two forward edges contact the DUT terminal for decreasing or eliminating the stray serial impedance (SSI) in series with the effective serial resistance (ESR) of the DUT.
A contact-holding structure mountable on the component testing system supports the contacts in side-by-side relationship for independent movement of the first, second, and third forward edges toward and away from the DUT terminal. A first spring bias the first and third forward edges toward the DUT terminal independently of the second forward edge, while a second spring biases the second forward edge toward the DUT terminal independently of the first and third edges, That arrangement helps further insure that at least two forward edges of the contacts bear against the DUT terminal for decreased SSI.
Thus, the invention alleviates problems of existing contactor assemblies. Direct replacement of an existing contactor assembly with a multi-contact, constant-force contact assembly constructed according to the invention significantly improves performance. One four-spring, twelve-blade embodiment of a multi-contact, constant-force contact assembly constructed according to the invention includes blade-type contacts separated by insulators. Roller contacts and pogo pin contacts fall within the scope of the invention. The following illustrative drawings and detailed description make the foregoing and other objects, features, and advantages of the invention more apparent.